Пример #1
0
  /**
   * Read an instruction from (byte code) input stream and return the appropiate object.
   *
   * @param file file to read from
   * @return instruction object being read
   */
  public static final Instruction readInstruction(ByteSequence bytes) throws IOException {
    boolean wide = false;
    short opcode = (short) bytes.readUnsignedByte();
    Instruction obj = null;

    if (opcode == Constants.WIDE) { // Read next opcode after wide byte
      wide = true;
      opcode = (short) bytes.readUnsignedByte();
    }

    if (InstructionConstants.INSTRUCTIONS[opcode] != null)
      return InstructionConstants.INSTRUCTIONS[
          opcode]; // Used predefined immutable object, if available

    /* Find appropiate class, instantiate an (empty) instruction object
     * and initialize it by hand.
     */
    Class clazz;

    try {
      clazz = Class.forName(className(opcode));
    } catch (ClassNotFoundException cnfe) {
      // If a class by that name does not exist, the opcode is illegal.
      // Note that IMPDEP1, IMPDEP2, BREAKPOINT are also illegal in a sense.
      throw new ClassGenException("Illegal opcode detected.");
    }

    try {
      obj = (Instruction) clazz.newInstance();

      if (wide
          && !((obj instanceof LocalVariableInstruction)
              || (obj instanceof IINC)
              || (obj instanceof RET))) throw new Exception("Illegal opcode after wide: " + opcode);

      obj.setOpcode(opcode);
      obj.initFromFile(bytes, wide); // Do further initializations, if any
      // Byte code offset set in InstructionList
    } catch (Exception e) {
      throw new ClassGenException(e.toString());
    }

    return obj;
  }
Пример #2
0
 /** Read needed data (e.g. index) from file. */
 protected void initFromFile(ByteSequence bytes, boolean wide) throws IOException {
   length = 3;
   b = bytes.readShort();
 }